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This work concentrates on the design parameters of a turbine blade for a small-scale solar chimney plant. The pitch angle (θ), relative wind angles (ϕ and ψ), lift force (FL) and relative chord length (lcr) of the turbine blade are determined. Betz and Bernoulli's theories were used for estimating and optimizing the above blade parameters. The coefficients of power, drag, lift and thrust forces are estimated and analyzed. Two wind speeds were considered. One represented higher speed (10 m/s) and the other for lower speed (2 m/s). At 10 m/s, the required rotor diameter is drastically reduced for producing the same power output. At 2 m/s, θ, ϕ, ψ and FL were optimized and they are; θ = 18.4°, ϕ = 26.4°, ψ = 75.6° and FL = 0.0073 N for maintaining the maximum power (P) of 0.026 W. The required diameter for the rotor blade is estimated and is varied from 0.66 to 6.56 m for producing a power range of 1–100 W. At 10 m/s, the optimized parameters are; θ = 42.9°, ϕ = 50.94° and ψ = 20.39° and FL = 0.4082 N for reaching the maximum P of 2.538 W. The estimated results were validated with existing studies and observed a good match. [ABSTRACT FROM AUTHOR]

Traditional solar updraft power plants work during the daytime as it is dependent on solar radiation to generate electricity. Hence, energy productivity, efficiency, and performance are limited. This work presents a novel attempt to increase the productivity of a traditional solar updraft system by combining it with a downdraft technology in one system, the Twin-Technology Solar System (TTSS). The TTSS comprises two co-centric inner and external solar towers, turbines, water sprinklers, and a collector. The inner tower works as a traditional solar updraft system, where the air is heated under the collector due to irradiance and then moved up the chimney due to the pressure column. While the external tower creates a downdraft wind by spraying water at the hot ambient air at the top of the tower. The hot air instantly absorbs the water and descends the tower to interact with the turbines at the bottom to produce electricity. This mode is independent of solar irradiance and can operate day and night. Hence, the TTSS generates electricity, daytime and night. A mathematical simulation model was developed based on the proposed system's energy and mass balance equations to assess performance. The TTSS generated 752,763 kWh of electricity annually, 2.14 folds higher than a traditional solar updraft system. Consequently, a reduction of 677 tons of CO2 was achieved with production. The design is suitable for deployment in hot and dry weather areas, such as remote villages and deserts. Future work will investigate introducing other technologies to boost the TTSS performance.

A big hurdle to using solar chimneys for power generation is their low overall efficiency, which is measured by how effectively energy is converted at different stages of the system. While a taller chimney might help, it is expensive and complex to implement. To address this issue, a new study explored the possibility of using a thermal absorbing assembly at the top of the chimney to increase its efficiency without increasing its height. The study presented both experimental and numerical data on this approach, looking at changes in temperature and heat gains as performance indicators. By adding this low-cost and simple fixture, the study found that the temperature before the chimney outlet increased, and the stack effect was strengthened. The rise of air temperature posed an increase of up to 83.1% by experimental assessment and an increase of 12.75% by numerical assessment with the added fixture of the heat trap. [ABSTRACT FROM AUTHOR]

The current investigation provides information about solar updraft tower power plants, SUTPPs (also called solar chimney power plants, SCPPs), which form a unique method of solar-powered electricity production through a ducted wind turbine driven by induced airflow as a result of solar heating. The investigation is conducted using numerical modeling via the system-level simulation tool Aladdin (developed and released freely by the Institute for Future Intelligence, IFI) for solar energy systems, wind energy systems, or the built environment. The Aladdin energy simulator is first evaluated here by comparison with published experimental and numerical results corresponding to the historical 50 kW prototype SUTPP that was successfully tested in Manzanares (Spain) between 1982 and 1989. This prototype has a height of about 195 m for the chimney (the updraft tower) and a radius of about 122 m for the solar heat absorber (the solar air collector or the greenhouse). Next, various climate and performance characteristics are investigated and contrasted for nine different locations around the world with a similar latitude of 24°, which is within the sunbelt, assuming that the same Manzanares SUTPP prototype geometry is employed in these locations. These nine locations are Muscat (Oman), Al Jawf (Libya), Riyadh (Saudi Arabia), Karachi (Pakistan), Ahmedabad (India), Havana (Cuba), Culiacán (Mexico), Dhaka (Bangladesh), and Baise (China). The energy generation intensity (EGI) for the Manzanares-type solar updraft tower power plant in these nine examined locations was between 0.93 kWh/m2 per year (in Baise) and 2.28 kWh/m2 per year (in Muscat). Also, Muscat had the smallest seasonality index (maximum-to-minimum monthly electric output) of 1.90, while Baise had the largest seasonality index of 4.48. It was found that the main limitation of the overall SUTPP energy conversion efficiency is the chimney efficiency (the process of accelerating the air after entering the chimney). This study concludes that solar updraft towers (SUTs) cannot compete with existing mature and modular renewable energy alternatives, particularly photovoltaic (PV) panels, if the aimed use is commercial utility-scale electricity generation. Instead, SUTs may become attractive and achievable if viewed as hybrid-use projects by serving primarily as a large-scale greenhouse area for agricultural applications while secondarily allowing energy harvesting by generating clean (emissions-free) electricity from the incoming solar radiation heat. [ABSTRACT FROM AUTHOR]

This work proposes a new chimney design that allows for the development of a multi‐stage solar updraft tower (SUT). The new design consists of two successive divergent chimneys. A 3D model was established to inspect the air flow behaviour within the SUT in six configurations: four multi‐stage systems with four divergence angles of the second stage were compared to the simple conventional SUT and the simple SUT with a divergent chimney. The new SUT performs better than the conventional one, while the two‐stage solar tower multiplied the system efficiency. Two high‐velocity zones appeared for the two‐stage SUT, whereas one zone occurred for the conventional system. The velocity in the two zones achieved a significant value, like that of the conventional system. In addition, the second stage's divergence angle directly impacts the velocity value inside the two stages. The static pressure distribution varies with the change in chimney design. The depression area occurs twice for the multi‐stage SUT in the inlet of each stage. [ABSTRACT FROM AUTHOR]

Three different models were developed to examine the flow and thermodynamic characteristics of the solar updraft tower (SUT) power plant and the best model is proposed. A step is taken to find the location of the turbine to absorb maximum kinetic energy. It is found that the maximum and average air velocities inside model-I were higher (3.06 and 1.63 ms−1, respectively) compared to model–II (2.4 and 1.34 ms−1) and model-III (2.9 and 1.57 ms−1). The maximum air temperature inside the model-II was higher (322 K). Turbulent kinetic energy, power produced and overall efficiency were the best in model–II than the other two models. The present outcomes were validated with the literature data and observed a good match.

The solar updraft towers harnessing solar energy are a sustainable and economical source of power, however, they suffer from low collector efficiency. Geometric characteristics have a large effect on the plant’s efficiency. One of the lesser-studied parameters that affect the flow behavior, and the performance of the plant is the chimney wall profile. A novel concept of parabolic wall profiles is introduced in this study using inner parabolic chimney profile (IPCP) and outer parabolic chimney (OPCP) configurations. For this purpose, the plant is modeled numerically and validated with the experimental data from the Manzanares prototype. The influence of parabolic profiles is studied at 0° to 3° chimney diverging angle (CDA) and 0° to 10° collector roof angle (CRA). The convergent effect of IPCP resulted in increased performance in contrast to OPCP. The appearance of large eddies creating a recirculation region near the base of the chimney is significantly decreased by using IPCP. The IPCP also resulted in an elevated performance when the effect of CDA and CRA is included resulting in a 12.1% increased power output. The IPCP at 1° CDA and 6° CRA is found to be the optimum among the studied configuration resulting in 80.6% and 80.7% increased power output and collector efficiency respectively. The proposed design resulted in smoother flow with smaller eddies, better thermal characteristics, and improved performance of the plant.

This work aims to analyse the performance of the SUT power plant in the environmental conditions of Nagpur and develop machine learning (ML) model to predict the power output of the SUT power plant. The developed ML model readily predicts the power output without rigorous calculations. Regularised polynomial regression with multiple variables technique was used to develop the ML model. Optimum values of the regularisation parameter, degree of the polynomial and the number of training examples were obtained from learning curves. A mathematical model of the SUT power plant is developed for analysing the performance of the SUT power plant and collecting training datasets for the ML regression model. The mathematical model analysed the effect of variation in chimney height, chimney and collector radius on SUT’s performance and flow parameters. The results demonstrate that raising the height and radius of the chimney and collector radius enhances the power generation of the SUT power plant. The monthly average power output was observed to be maximum in June and July and minimum in December. Calculation of the power output is done from 5.00 AM to 6 PM. The maximum power production in June is 120 kW and in May is 117 kW. The average annual power output is around 64 kW. [ABSTRACT FROM AUTHOR]

The current investigation provides information about solar updraft tower power plants, SUTPPs (also called solar chimney power plants, SCPPs), which form a unique method of solar-powered electricity production through a ducted wind turbine driven by induced airflow as a result of solar heating. The investigation is conducted using numerical modeling via the system-level simulation tool Aladdin (developed and released freely by the Institute for Future Intelligence, IFI) for solar energy systems, wind energy systems, or the built environment. The Aladdin energy simulator is first evaluated here by comparison with published experimental and numerical results corresponding to the historical 50 kW prototype SUTPP that was successfully tested in Manzanares (Spain) between 1982 and 1989. This prototype has a height of about 195 m for the chimney (the updraft tower) and a radius of about 122 m for the solar heat absorber (the solar air collector or the greenhouse). Next, various climate and performance characteristics are investigated and contrasted for nine different locations around the world with a similar latitude of 24°, which is within the sunbelt, assuming that the same Manzanares SUTPP prototype geometry is employed in these locations. These nine locations are Muscat (Oman), Al Jawf (Libya), Riyadh (Saudi Arabia), Karachi (Pakistan), Ahmedabad (India), Havana (Cuba), Culiacán (Mexico), Dhaka (Bangladesh), and Baise (China). The energy generation intensity (EGI) for the Manzanares-type solar updraft tower power plant in these nine examined locations was between 0.93 kWh/m2 per year (in Baise) and 2.28 kWh/m2 per year (in Muscat). Also, Muscat had the smallest seasonality index (maximum-to-minimum monthly electric output) of 1.90, while Baise had the largest seasonality index of 4.48. It was found that the main limitation of the overall SUTPP energy conversion efficiency is the chimney efficiency (the process of accelerating the air after entering the chimney). This study concludes that solar updraft towers (SUTs) cannot compete with existing mature and modular renewable energy alternatives, particularly photovoltaic (PV) panels, if the aimed use is commercial utility-scale electricity generation. Instead, SUTs may become attractive and achievable if viewed as hybrid-use projects by serving primarily as a large-scale greenhouse area for agricultural applications while secondarily allowing energy harvesting by generating clean (emissions-free) electricity from the incoming solar radiation heat.

This study investigates the possibility of applying a large-scale solar updraft tower power plant in India with local ground conditions as an environmentally friendly and economically viable energy source. A reference model Solar Updraft Tower Power Plant (SUTPP) is constructed to examine the influence of the most prominent plant dimensional parameters, including collector radius (RCollector), tower height (HTower), and tower radius (RTower) with dimensional limits and intervals on the power output of the SUTPP. Udat, Rajasthan, India, is used as a reference location for meteorological conditions to evaluate SUTPP power output equations for a ranging power output, with position coordinates of 27°35′ and 72°43′. Multiple simulations for the objective function are carried out, and the outcomes are compared to the optimized dimensions of each set of plants. The model examines the effect of variation in ambient, plant geometry, and material conditions on power output and analyzes efficiency and power output for optimizing configuration. There exists no definitive approach to determining the proper correlation between the geometrical parameters of a SUTPP with optimized power output. For a fixed power output, the tower radius (RTower) serves as the most influencing dimensional parameter in SUTPP performance. A change in tower height (HTower) has a detrimental impact on SUTPP output and performance. An initial increase in collector radius (RCollector) has a positive influence on SUTPP performance; however, this effect reduces as collector radius (RCollector) increases. [ABSTRACT FROM AUTHOR]

This paper focuses on the feasibility of the solar updraft tower (SUT) plant, a solar thermal power-production application, through numerical studies. To assess the feasibility, the climatic conditions of 23 possible Indian cities have been taken into consideration and 10 of them have been selected for the analysis, based upon the various solar-related parameters. The numerical model developed is based on the dimensions of the Manzanares (Spain) plant. Through CFD techniques, the flow through the SUT plant is simulated by taking local weather data as boundary conditions. The absorber plate temperature, the temperature near the chimney base of the model and the velocity of the air have been determined and analyzed. Hourly and yearly power potentials, the collector and the overall efficiencies of the plants have also been estimated for different cities and optimized locations have been proposed. The results obtained from the analysis show that the selected regions are able to produce a theoretical power output of 60.94 kW on average for all the cities. Bhavnagar plant produces the highest among all the cities with an hourly potential of 69.897 kW. However, the annual power production of the plants in all the cities is found to be 164.4 MWh on average with Goa having the highest potential of 177.86 MWh. The estimated flow parameters are validated with the published data and noticed a good agreement. [ABSTRACT FROM AUTHOR]

Three different models were developed to examine the flow and thermodynamic characteristics of the solar updraft tower (SUT) power plant and the best model is proposed. A step is taken to find the location of the turbine to absorb maximum kinetic energy. It is found that the maximum and average air velocities inside model-I were higher (3.06 and 1.63 ms−1, respectively) compared to model–II (2.4 and 1.34 ms−1) and model-III (2.9 and 1.57 ms−1). The maximum air temperature inside the model-II was higher (322 K). Turbulent kinetic energy, power produced and overall efficiency were the best in model–II than the other two models. The present outcomes were validated with the literature data and observed a good match. [ABSTRACT FROM AUTHOR]

Solar updraft tower (SUT) plant is one of the potential technologies for carbon-free power generation. However, a conventional SUT plant is not economical due to its lower thermal performance. The present work provides an in-depth numerical investigation and thereby enhancing the thermal performance of the SUT plant. The real SUT plant (Manzanares, Spain) dimensions were considered for this three-dimensional analysis. Two models of the SUT plant were developed; Case 1 having no fillet, Case 2 having a 45° square fillet. Comparative analysis was done between Case 1 and Case 2 on various performance characteristics such as turbine power (P the), collector and overall efficiencies (η coll , η o). Higher updraft velocity (about 38.5% rise) was observed due to the provision of fillet in case 2. Also, case 2 produced a P the of 141 kW, η coll of 62% and η o of 0.25% which are with an enhancement of 73.3%, 48.44% and 72.4%, respectively. These abrupt variations in performance parameters proved that the fillet makes much impact on the SUT system and therefore it must be built on the base of the chimney. The results were compared with the existing experimental data and found promising agreement. • The effect of fillet near the chimney base of solar updraft tower (SUT) plant was analyzed. • Two SUT models of without and with fillet were modelled and simulated. • 38.5% of velocity enhancement was noticed in SUT with fillet case. • An abrupt enhancement was noticed in all flow and performance parameters. • The overall efficiency of the plant with fillet was improved to 72.4%. [ABSTRACT FROM AUTHOR]

This study investigates the possibility of applying a large-scale solar updraft tower power plant in India with local ground conditions as an environmentally friendly and economically viable energy source. A reference model Solar Updraft Tower Power Plant (SUTPP) is constructed to examine the influence of the most prominent plant dimensional parameters, including collector radius (RCollector), tower height (HTower), and tower radius (RTower) with dimensional limits and intervals on the power output of the SUTPP. Udat, Rajasthan, India, is used as a reference location for meteorological conditions to evaluate SUTPP power output equations for a ranging power output, with position coordinates of 27°35′ and 72°43′. Multiple simulations for the objective function are carried out, and the outcomes are compared to the optimized dimensions of each set of plants. The model examines the effect of variation in ambient, plant geometry, and material conditions on power output and analyzes efficiency and power output for optimizing configuration. There exists no definitive approach to determining the proper correlation between the geometrical parameters of a SUTPP with optimized power output. For a fixed power output, the tower radius (RTower) serves as the most influencing dimensional parameter in SUTPP performance. A change in tower height (HTower) has a detrimental impact on SUTPP output and performance. An initial increase in collector radius (RCollector) has a positive influence on SUTPP performance; however, this effect reduces as collector radius (RCollector) increases.

Summary: A 3D computational model was developed to investigate the influence of divergence angle of chimney (θch) on the flow and performance characteristics of solar updraft tower (SUT) plant. The diameters of the chimney (Dch)i and air entrance gap (e) selected for numerical simulations were 0.6 m and 0.1 m, respectively. Parametric study was carried out by varying θch from 1° to 5° for different solar fluxes (600‐1200 Wm−2) and the outcomes were compared with cylindrical chimney (θch = 0°) SUT (CC‐SUT) plant. The effect of ambient temperature on the performance was also studied. A turbulent model (renormalization group k‐ɛ) was incorporated for considering the turbulence effect. Discrete ordinates model was used for estimation of radiation heat transfer inside the setup. It was found that the velocity of air at the chimney base was enhanced by 59.4% compared to a CC‐SUT plant. From the parametric study, it was observed that θch = 2° gives superior performance to the system than any other angle. Also, maximum performance was achieved at higher solar flux (I). The average absorber plate temperature increased from 313.3 to 350.3 K with increase in solar flux from 600 to 1200 Wm−2. The overall efficiency, and theoretical and actual power outputs of the divergent chimney‐SUT system were estimated and they were 0.0278%, 4.01 and 2.68 W, respectively. The net exergy efficiency (ψnet) of the system increased from 0.98% to 19.41% with increase in I from 600 to 1200 Wm−2 at θch = 2°. There was 55.2% increase in ψnet when θch increased from 1° to 2° and at I = 1200 Wm−2. Correlations were developed for the prediction of ψnet for different θch and at different I. [ABSTRACT FROM AUTHOR]

• 15 models were developed with different collector angle (θ) to analyse the impact. • Velocity, pressure, power, collector and overall efficiencies were estimated. • Enhancement of air velocity and theoretical power were noticed at θ = 6°. • θ more than 6° created extensive recirculation and vortices inside the canopy. • A correct turbine location was proposed for Manzanares plant. In this paper, a three-dimensional turbulent study was carried out on Manzanares (Spain) plant to study the effects of collector inclination angle (θ). Different ranges of θ (30–0°) with more than 15 models were considered for the analysis. An optimized θ has been proposed based on the estimated parameters such as air velocity, pressure drop, absorber and air temperatures, power developed, collector efficiency, and overall efficiency (η coll and η o). At θ = 6°, an increment of 9.16% in theoretical power (P th) and a 10.68% increase in air velocity were observed at the chimney base (CB) compared to the horizontal collector plant. Any further increase in θ (greater than 7°) resulted in recirculation of air particles within the collector canopy, leading to obstruction of flow. Any value of θ lesser than 6° resulted in a drop in the major outputs such as P th , η coll, and η o. Eventually, θ = 6° has been proposed as optimized inclination. The dynamic pressure difference was maximum at a chimney height of 2.5 m from CB; therefore, this was the preferred location for turbine fitment. The results were compared with the experimental data of the Manzanares plant, and a very favorable agreement was noticed. [ABSTRACT FROM AUTHOR]

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Solar vortex engine (SVE) is one of the novel alternative energy concepts which uses solar energy for creating artificial vortices. The working principle of SVE is the same as the solar updraft tower (SUT) plant. In the present study, a 3D computational model of SVE was studied to evaluate the flow parameters and power potential. The effect of the number of air entry slots (AESs) which is varied from 6 to 12 and the location of the turbine were studied and optimized. A turbulent, renormalization group (RNG) k-ɛ model was used to solve the governing equations. The flow parameters such as velocity, temperature and dynamic pressure for the optimum SVE with 8 AESs were 1.42 ms−1, 311.1 K and 1.58 Pa, respectively. The optimum height for the turbine was 0.702 m from the base plate (0.1 m from the top plate) and so that the turbine can harness maximum energy. The theoretical and actual powers for the optimum case (AESs of 8 and the turbine at 0.702 m) were 3.45 and 2.3 W, respectively. The study proved that SVE is a potential choice to replace the chimney of a solar updraft tower (SUT) plant for electricity generation. [ABSTRACT FROM AUTHOR]

This study analyzes the feasibility of implementing an integrated system for electricity and freshwater production, focusing on solar chimney technology as its main pillar. A preliminary study based on literature is carried out to analyze electrical generation and the heat transfer to the storage system of the solar chimney. In addition, a seawater thermal desalination is incorporated with the idea to increase the overall efficiency of the solar chimney. Furthermore, in order to address electricity and freshwater demand without interruption, a hydro-storage system with a water turbine is integrated. As a result, implementing an integrated system with a solar chimney as its main source of energy, the overall energy efficiency is obtained to be 8.4%, which is substantially higher than a single solar chimney.

Solar updraft tower (SUT) power plant is a unique system using solar energy, which consists of three main parts: the chimney, turbine, and collector. In tropical climate conditions, especially in Malaysia, the application of solar chimney can be deemed more competitive compared to other renewable energy systems. In this study, one prototype with a dimension of 3.5 m in diameter for the collector and 5 m height for the chimney, was built in Melaka, Malaysia. Vital parameters such as temperature field, pressure, humidity, and air movement were measured using data logger and stored using non-volatile memory. The most exciting finding was that the temperature and pressure difference was significantly seen during the experiment along the day. There was a significant surge for the humidity in the morning with an average of above 95% and the ambient temperature was approximately 35 °C due to low solar radiation. The humidity kept decreasing after sunrise due to the greenhouse effect produced in the solar collector. With the collection of these critical parameters, a solar chimney power plant was adequate to function and generate power from solar radiation in a country such as Malaysia, which is based in the equatorial region. These studies are limited as the analysis focused mainly for high radiation and did not investigate efficiency during low solar radiation. The addition of heat storage underneath the collector with current techniques is another direction of research for continuous system operation, particularly during low solar radiation. It is proposed that the synthesis of these factors should be extensively explored in future studies coupled with the application of heat storage. [ABSTRACT FROM AUTHOR]

A numerical analysis has been performed to examine and assess the flow and performance characteristics of the solar updraft tower (SUT) power plant. A realistic domain (geometry and mesh) of the flow model was generated and simulations were run with the help of ANSYS FLUENT 16.0 CFD package. A turbulent, realizable (k–ε) and discrete ordinates radiation techniques were taken into consideration to solve the governing equation. The maximum air velocity of 3.27 m s−1 was noticed at 200 mm above the chimney base (CB). The mean velocity at CB was 1.8 m s−1. The highest air temperature of the absorber plate was 323 K, and it was at the centre of the absorber plate. The average air temperature inside the setup was 306.7 K. The power generated from the plant, chimney efficiency and overall efficiency of the SUT setup were evaluated to be 0.38 W, 0.018% and 0.005%, respectively. 24% velocity increase and 70% power output increase were noticed when solar flux increased from 650 to 1150 W m−2. Exergy analysis was performed. The results were compared with existing studies and were found to be in good agreement. [ABSTRACT FROM AUTHOR]

The current study is aimed at harnessing solar power through solar updraft tower (SUT) and explored the local environmental factors conducive to SUT installation. The SUT collects solar insolation to raise the air velocity, which is then allowed to pass through a ducted turbine. An alternator is installed with the air turbine to generate electricity. The study presents a performance analysis of SUT based on local thermal radiation and wind velocity. Three-dimensional numerical modelling of SUT is carried using computational fluid dynamics (CFD) solver. The model is validated with the experimental results available in the open literature. The collector temperature profile obtained through CFD modelling matches well with the experimental results. A maximum temperature rise of 20 °C was ob-served in the collector modelled and solved numerically using CFD solver. The air velocity increases as the flow move from the collector periphery to the center of the SUT and reach to its maximum just before the center of the SUT. However, for the chimney, the temperature was observed to be increased continuously due to its continuous heating through the chimney walls, which receives solar radiation. The performance of SUT is examined with the change in inlet air velocity based on the local conditions in the Sultanate of Oman. [ABSTRACT FROM AUTHOR]

The relationships between temperature rise, flow rate, and power output of turbine are presented for a small solar chimney unit. An experimental solar chimney system was constructed at Engineering Faculty of Trakya University in Turkey. Solar radiation, temperature rise, chimney inlet velocity, air flow rate, and power output were monitored. Solar chimney power output can be controlled by air flow management and maximum power point can be achieved for different operating conditions. Results showed that it is possible to obtain up to 50% more power output by using an air flow controller in solar chimney systems. Typical temperature rises for 400–600 W/m2 solar radiation is found to be in the range of 12–15°C. Power is changed in the range of 30–60 W according to different flow rates. [ABSTRACT FROM AUTHOR]

This paper investigates a simplified and fast numerical model of a solar updraft tower. The model applies a novel approach to the calculation of heat transfer from the outside environment to a collector in the tower. Complex calculations of heat transfer are replaced by a properly defined heat ux boundary condition - the value of which depends on the time of day and meteo- rological conditions. The model was validated by experimental results from a pilot plant in Manzanares, Spain. Calculations were performed in order to investigate the effects of the chim- ney's height and the density of the solar radiation. Both of these dependencies were found to be logarithmic. The require- ments for a 250 kW plant in various locations with different meteorological conditions were analyzed. [ABSTRACT FROM AUTHOR]

Abstract Solar updraft tower (SUT) is a simple power plant in which ventilation of heated air inside a channel drives a turbine. This system is recognised as suitable for areas with abundant solar radiation. As a result, there is no extensive research on the performance of SUTs under mild solar radiation. Studies show that strong ambient crosswinds can affect the performance of a SUT. In this paper, the efficiency of SUTs in areas which benefit from strong winds, despite low solar radiation, is investigated through numerical modelling. Comparison is made between the efficiency of a commercial-scale SUT in Manzanares (Spain) with intensive solar radiation, and one of the same size potentially located in the windy and mild climate of Orkney Islands in Scotland. The results show that ambient crosswinds can increase internal air speed and efficiency of a SUT by more than 15% and 50%, respectively. Consequently, such a SUT in Orkney can offer more than 70% of the efficiency of the one in Manzanares. The results show that, for a given power capacity, a wind turbine enclosed in a SUT can be considered as an alternative to a number of conventional wind turbines installed at height in the open air. Highlights • Strong ambient crosswinds can increase the efficiency of SUTs by more than 15%. • A large SUT in a windy climate can have 70% of the efficiency of the one in a sunny climate. • A wind turbine enclosed in a SUT is more efficient than conventional wind towers. [ABSTRACT FROM AUTHOR]

An experimental analysis of the solar updraft tower (SUT) with convergent chimney was undertaken by using different absorbers. Four different types of absorber materials were used in the experiment to store the solar intensity and exchanging it to the air being heated. The SUT comprised the three basic parts named as the solar collector, the tower or chimney and the turbine. An analysis for the solar updraft tower has been carried out, which describes the performance of solar updraft tower based on energy and exergy analysis. The maximum temperature distinction between ambient air and collector outflow was obtained in the case of SUT with small stone pieces (16.4 °C). The maximum average collector efficiency, collector exergy efficiency and overall efficiency of the SUT were acquired with the small stone pieces. The benefit of SUT system is that it would be favorable in the region with magnificent sunbeams to satisfy the demand of electricity. [ABSTRACT FROM AUTHOR]

Abstract A computational model is developed to investigate the influence of geometrical configurations such as chimney height (H ch), absorber plate diameter (D ap) and collector plate angle (θ cr) on flow and performance characteristics of solar updraft tower (SUT) plant. The diameter of the chimney (D ch) and air entrance gap (e) selected for numerical simulations are 0.6 m and 0.1 m, respectively. Parametric study is carried out by varying H ch of 3–8 m, θ cr of 20°-35° with an increment of 5° and D ap of 3.5–12 m. A turbulent model (RNG k-ɛ) is incorporated for considering turbulence effect and Discrete ordinates (DO) model incorporated for estimation of radiation heat transfer inside the setup. It is found that a slight decrease of temperature and increase of air velocity when θ cr is increased. It is noticed that air velocity is enhanced (up to 44%) while the H ch is increased from 3 to 8 m. Power output, overall, chimney and exergy efficiencies are estimated. Correlations are developed to estimate the performance parameters in terms of geometrical configurations. From the parametric study, it is concluded that for the D ch and e of 0.6 m and 0.1 m, respectively, better performance can be achieved at a H ch of 7 m, θ cr of 30° and D ap of 5 m. Highlights • 3D numerical model is developed to estimate the flow and performance parameters. • The effect of chimney height, collector roof angle and absorber plate diameter are analysed. • There is 44% velocity enhancement when chimney height increased from 3 to 8 m. • Exergy analysis of SUT plant is made. • New set of correlations are developed based on the numerical results. [ABSTRACT FROM AUTHOR]

Solar updraft tower (SUT) is a viable option to produce electrical energy from solar energy. Extensive studies needed to estimate the flow parameters and analyse this set-up. A 3D numerical model is developed to analyse the flow parameters such as pressure, temperature and velocity of SUT plant. Effect of geometrical parameters such as chimney height and collector roof angle is studied numerically in this work. The diameter of absorber plate and chimney as 3.5 m and 0.6 m and the collector roof angle, chimney height and inlet gap as 30º, 6 m and 0.1 m, respectively, are selected for numerical simulation. A parametric study is performed for varying chimney heights from 3 to 8 m and collector roof angle 20º-35º with an increment of 5º each case. The airflow inside the SUT is turbulent, renormalization group (RNG) k-ε model is selected, and (discrete ordinates) DO model is incorporated for evaluation of radiation effect inside the domain. From the simulation results, it is concluded that when collector roof angle is increased, air velocity is increased and also air temperature is slightly dropped. It is found that there is 31% velocity enhancement when the chimney height is increased from 3 to 8 m. [ABSTRACT FROM AUTHOR]

Highlights • Seven questions about SCPP are presented in this work. • Current understanding about SCPP are described in this work. • Several suggestions are proposed for future studies of SCPP. Abstract Interest in solar chimney power plant (SCPP) has seen resurgence due to the continuously increasing awareness on environmental concerns, particularly greenhouse gas emissions from fossil fuels, since the 21st century. Although remarkable advances in the understanding of SCPP have been achieved through extensive theoretical, experimental, and numerical studies with different focuses on various aspects of the SCPP technology, no industrial scale SCPP has been built. In response to these new scientific advances and challenges for commercialization, seven questions, including parameter influences, turbine design, flow and heat transfer characteristics, similarity analysis, and hybrid systems, are presented in this work. In addition, answers and current understanding are included to provide succinct links to latest knowledge and identify areas that require further research. [ABSTRACT FROM AUTHOR]

Abstract A 3D numerical model is developed for solar updraft tower to identify the effect of thermal energy storage system. Flow parameters such as temperature, velocity, pressure, and density are estimated, analyzed and compared for 2 different models, model - 1 (without thermal energy storage) and model −2 (with thermal storage). The collector diameter of 3.5 m, chimney height of 6 m, chimney diameter of 0.6 m, inlet gap of 0.15 m, slope of the collector 30° are the dimensions considered for model - 1. Model – 2 consists of the same dimensions of model – 1 with additional thermal energy storage system. Sand-rock mixture is considered as energy storage material and it has the thickness of 0.15 m and diameter of 3.5 m. Numerical simulations are performed under steady state condition for both the models at various times (10.00 a.m., noon, 1.00 p.m., 2.00 p.m. and 4.00 p.m.) in a day and for model – 2 up to 8.00 p.m. Results are compared with experimental and theoretical data from literature and found that the results are matching. Performance parameters such as power output, collector efficiency and overall efficiency of system were estimated and it was found that the values of model – 2 are lower because of heat stored by thermal storage device. Maximum power output for both models (79.92 W for model – 1 and 63.8 W for model – 2) was obtained at 1.00 p.m. The addition of thermal storage system enhanced the plant operation time till 8.00 p.m. Highlights • 3D numerical model is developed to identify the effect of thermal energy storage (TES). • Two models - without (model −1) and with thermal energy storage (TES) (model −2) were developed. • Maximum velocity and temperature were achieved in model – 1 (6.8 m/s and 308.5 K) compared to model – 2 (4.24 m/s and 306.5 K). • At 8.00 p.m., model – 2 reached equilibrium state. • Maximum power outputs were 79.92 and 63.8 W for model – 1 and model – 2, respectively. [ABSTRACT FROM AUTHOR]

Highlights • Energy/exergy/exergoeconomic analysis is performed for SCPP-WTE integrated system. • The effect of important parameters on CO 2 emission is evaluated. • Multi-objective optimization based on genetic algorithm is implemented. • Exergy efficiency and total cost rate are 7.56% and 406.8 $/h at optimum point. • Scatter distribution is depicted to have better outlook of optimum parameters. Abstract In this study, an integrated renewable energy system is proposed by integrating Tehran's waste-to-energy plant with a solar chimney power plant. The integration is performed by exploiting warm air of the condensers cooling air for injecting under the turbine of solar chimney power plant. The proposed system is analyzed from energy, exergy, exergoeconomic, and environmental viewpoints through the parametric study. Exergy efficiency, net power output, solar chimney power plant power output, total product cost and cost rates of the system are plotted and compared during the night and daytime. Additionally, influence of the effective parameters is examined on the CO 2 emissions indicator. Subsequently, the proposed system is optimized by multi-objective optimization method using a developed MATLAB code based on a genetic algorithm. Four effective design parameters are presumed for multi-objective optimization purpose and exergy efficiency along with total cost rate are considered as the objective functions. Accordingly, a group of the optimal solution points is gathered as a Pareto frontier and the most favorable solution points are ascertained from an exergy/exergoeconomic viewpoints. In addition, a point which is well-balanced between the conflicting objectives is selected as the final solution. Eventually, scatter distribution of the effective parameters are presented to have a better outlook of optimal ranges of the parameters. Results indicate that exergy efficiency of the system is higher during the nighttime while total product cost is lower during the daytime. Results further indicate, turbine inlet pressure has the highest impact on the CO 2 emissions and the solar chimney power plant has the highest exergy destruction. Results of the multi-objective optimization demonstrate that at the best solution point, exergy efficiency and total cost rate of the system are 7.56% and 406.8 $/h. Furthermore, analyzing scatter distribution of the effective parameters reveals that higher values of the superheater temperature difference may be a better choice for designing the system. [ABSTRACT FROM AUTHOR]

Highlights • It gives a complete modelling and fast simulation tool for the design and the operation of a solar thermal power station. • It refers to a highly complex fluid dynamic problem involving humidity, friction, heat transfer etc. • It involves a significant non trivial modelling part (in order to reduce the problem to a treatable simulation problem). • It uses a small Mach number asymptotics to simplify the model and to accelerate significantly the simulation. Abstract A model to describe a solar chimney power plant with a generally sloped collector field and for the general situation of humid air is presented. This is a significant development of existing simple models for solar updraft towers with planar collector fields for the situation of purely dry air. The model describing the gas dynamics in the collector and in the chimney includes a turbine model, friction and heat transfer losses, evaporation and condensation models etc. However, the relevant physics can be modeled in one space dimension. It is the result of a fully compressible gas dynamic model in the small Mach number limit. A numerical algorithm is defined which admits very fast simulations. Therefore optimization procedures can easily be applied. Numerical results on optimization with respect to geometric and physical parameters which may be considered both in the planning and the operational phase are presented. The results are compared qualitatively and – if available – quantitatively to prototype data and to simulations from the literature. [ABSTRACT FROM AUTHOR]

A 3D numerical model is developed to estimate and analyze the flow and performance parameters of solar updraft tower (SUT) plant. The effects of geometrical parameters, such as chimney height and collector roof angle are studied. A turbulent, renormalization group (RNG) k-ε model and discrete ordinates (DO) model is used to solve the governing equations. It is concluded that with an increase in collector roof angle, air velocity increases but air temperature decreases. There is 31% velocity enhancement when the chimney height is increased from 3 to 8 m. The overall, chimney and collector efficiencies and power output are estimated to be 0.00354%, 0.0465%, 81.4% and 0.255 W, respectively. [ABSTRACT FROM AUTHOR]

This paper presents a thermodynamic analysis of the drying of bananas inside a small-scale prototype solar updraft tower in Belo Horizonte, Brazil. A model based on the first and second laws of thermodynamics was developed, using the ambient conditions and airflow parameters data obtained in the experimental prototype. The exergy rates were determined, and it was concluded that the incident solar radiation plays an important role on the drying process of bananas, the higher the solar radiation, the higher the exergy rates. The exergetic efficiency was compared to that obtained without products inside the solar updraft tower, and it was found that the exergetic efficiency increased from about 20% to 27% with load. [ABSTRACT FROM AUTHOR]

A solar updraft power plant (SUPP) technology is a promising large-scale utilizing technology of renewable energy resource. Since the feasibility of the technology was demonstrated by the successful operation of the Manzanares pilot prototype, the plant performance has been widely studied. This paper carries out computational fluid dynamics (CFD) simulations of an SUPP, analyzes the characteristics of the mean and fluctuating wind pressures on the internal and external surfaces of solar updraft tower (SUT) and the upper and lower surfaces of solar collector roof, examines the effects of the SUT and baffle to the pressure on the roof's upper and lower surfaces, and discusses the effects of vortexes to the plant surface pressures and the potential effect of vortex shedding to the tower structural dynamics. It is hoped that this paper will guide further study and accurate design on this interesting power plant. [ABSTRACT FROM AUTHOR]

• A novel solar updraft tower with windcatcher has been studied. • Transpired solar collectors are used in the concept. • Two counter-rotating vertical axis turbines are used in the concept. • Diffuser-shaped downdraft tower acclerated incoming wind up to 2.5 times. • Power generation increased 8 times compared to traditional updraft solar tower. In this study, a novel solar updraft tower system that combines updraft and downdraft is examined, its functional principle is explained and its performance is presented. A prototype was built at Faculty of Engineering of Trakya University in Edirne Türkiye in 2017. The concept includes counter-rotating dual drag type vertical axis turbines, wind catchers, three prismatic diffuser towers and sloped transpired solar collector. The results showed that the downdraft wind catcher integration increased annual energy production by 8 times compared to a conventional solar updraft tower. In the diffuser-shaped downdraft tower, the incoming wind accelerated up to 2.5 times. The power potential, which is 160 W for the conventional system, becomes 83 kW at a wind speed of 10 m/s and a downdraft pressure coefficient of 1.0. [ABSTRACT FROM AUTHOR]